FIG. 9 shows the configuration of the bones of a right human foot as seen from the bottom side of the foot. FIG. 11 shows the configuration of the bones of a right human foot as seen from the instep side. As shown in FIG. 9 and FIG. 11, the bones of the human foot consist of the tarsals N3, which include the calcaneus Q1, the talus Q2, the navicular Q3, the cuneiform bones Q4-Q6, and the cuboid Q7, as well as the 5 metatarsals N2, and the phalanges N1.
The joints of the bones that form the foot are strongly bound to each other by ligaments, and form the skeletal structure of the foot. Since a group of plantar muscles formed from soft tissues such as the metatarsal muscles, thenar muscles, and antithenar muscles is present on the bottom of the foot, the shape of the bottom of the foot further increases the stability. As shown in FIG. 10(b), longitudinal plantar arch P1 (arch in the longitudinal direction) and transverse plantar arch P2 (arch in the longitudinal direction) are formed on the bottom of the foot from these bones, ligaments, and group of plantar muscles.
As shown in FIGS. 9 and 10(a), the longitudinal plantar arch P1 is formed from an inside arch (inside longitudinal arch) which extends across the talus, the navicular, and the inside cuneiform bones to the first metatarsal N21, and from an outside arch (outside longitudinal arch) forming an arch which extends across the cuboid to the fifth metatarsal N22, the arch having a starting point of the calcaneal tubercle N31. On the other hand, as shown in FIG. 9 and FIG. 10(a), the transverse plantar arch P2 is formed from an anterior arch which extends from the first metatarsal N21 to the fifth metatarsal N22, and a primary arch which extends from the left side N32 to the right side N33 of the arch of the foot, including the 3 cuneiform bones.
Accordingly, the longitudinal planar arch P1 (inner longitudinal arch, outer longitudinal arch) formed from bones, ligaments, and a group of plantar muscles, and the transverse plantar arch P2 (anterior arch, primary arch) are formed on the bottom of the foot. The arch structures of the sole of the foot formed from these four arches do not represent independent entities, but rather, are mutually related in forming the arch of the foot, and serve as: 1) a spring to soften the impact of the foot touching the ground while walking; 2) to distribute the body weight over the entire foot; and 3) to play an important role in making for a smooth shifting of body weight. It is therefore thought that maintaining a normal shape for the longitudinal plantar arch P1 and the transverse plantar arch P2 is also related to preventing a variety of foot injuries.
However, when the plantar ligaments and the group of plantar muscles stretch excessively due to vigorous exercise and walking for long periods of time, it becomes impossible to maintain the arch shapes of the longitudinal plantar arch P1 and the transverse plantar arch P2 and a shock-absorbing effect is not sufficiently achieved during walking, thus it becomes impossible to achieve a sufficient spring-like function, consequently causing the feet to tire and the body to feel languid. Furthermore, since the bottoms of the feet are unable to absorb shock, this can affect the joints of the feet, the knees, and the groin. In severe cases, this excessive stretching may affect the hips and the shoulders, making it necessary to undergo treatment at a hospital.
Accordingly, there have been disclosed socks which aimed to restore an almost normal state to the transverse arch and to the longitudinal arch of the sole of the foot which had lost their shape or had been lost altogether due to shoes that did not fit.
For example, Japanese Laid-Open Patent Application No. 2005-3125121, a sock is disclosed having a structure in which there is provided an elastic expanding member in the width direction of the foot having a tension resistance force greater than other parts in at least a part corresponding to the side of the bottom of the foot of the transverse ligament, among the parts corresponding to the bottom side of the foot from the first to fifth materials, and a part corresponding to the dorsal side of the tarsals.
However, the sock of Japanese Laid-Open Patent Application No. 2005-3125121 gives priority to preventing the development of conditions such as poor blood circulation and chilblain, and does not provide an elastic expanding member for the entire periphery in the course direction of the sock. Therefore, since the position of the elastic expanding member slips while the sock is being worn, there is the problem in that the sock does not impart a continuous compressive force at the desired position, making it impossible to achieve much of an advantageous effect, even if an elastic expanding member is provided with the aim of restoring the transverse arch and the longitudinal arch.
In Japanese Laid-Open Patent Application No. 2006-225833 is disclosed a sock having a structure with a network of highly elastic areas which connect at least an area which traverses the arch portion and an area which traverses the upper portion of the calcaneus.
However, since the sock of Japanese Laid-Open Patent Application No. 2006-225833 imparts an upward force on the upper portion of the calcaneus from the position of the arch due to the highly elastic areas in an upper diagonal direction, but no consideration was given to protecting and restoring the transverse plantar arch and the sock fails to protect the longitudinal plantar arch by lifting the arch straight upward and to restore the longitudinal plantar arch to its original shape.
In addition, in the sock of Japanese Laid-Open Patent Application No. 2006-225833, since the highly elastic areas which are divided right and left by the arch portion are continued again from the back of the heel, when the sock is worn, it is possible to prevent it from slipping forward from the arch position, but a problem exists in that it is impossible to prevent the position of the highly elastic areas to slip backward from the arch position. Accordingly, since the position of the highly elastic areas slips while wearing the sock, it is impossible to continuously raise the arch.
The present invention was devised with the problems of conventional socks in mind, and has as one of its objects to provide a sock which is able to maintain a normal shape of both the longitudinal plantar arch and the transverse plantar arch formed by the bones of the foot, the ligaments, and a group of plantar muscles, by securely positioning compression areas at a suitable position on the foot, without the compression areas slipping when the sock is worn.